I obtained my PhD in Physics at Universidad de Chile on 1996 under the supervision of Professor Enrique Tirapegui. After a postdoctoral work with Professor L. Mahadevan at MIT on crumpling of thin films I joined the Universidad de Santiago. Thanks to a Fundacion Andes Fellowship and the support of the University of Cambridge, I had the opportunity on 2001 to be part of the research group of Professor L. Mahadevan who was working in the Department of Applied Physics and Applied Mathematics (DAMPT) at that time. On 2004 I rejoined the group of Soft Matter in Universidad de Santiago where I have been working until now.

My research is focused on the physics and geometry of thin surfaces. We have studied the crumpling, folding and wrinkling of soft and stiff elastic surfaces. Examples include the stretching of thin membranes to form wrinkles, the buckling of a sheet when pushed into a circular opening to form a d-cone, the folding of a circular latex membrane by rotation of its centre, etc.. We use analitical methods to understand the nature of these phenomena, and carry out simple experiments to help guide us.

Pollen grains folding.

Geometry of peeled surfaces.

Wrinkling of stretched surfaces.

The Geometry and Structure off PollenGrains

Pollen grains are beautifull structures that show an amazing range of variations between different species of plants. They have an outer wall, which is stiff, with one or more openings for the exit of the germinating pollen tube. This tube carries the reproductive cells from the pollen grain to the ovules inside the pistil. The openings are covered by a thin membrane designed to break under the pressure of the growing tube.

The most exiting physical phenomena behind pollen grains is their ability to close the openings by deforming the outer wall. Pollen grains detect changes of humidity and close the gates under dry conditions to keep water inside. The opposite happens when humidity conditions are fair enough; the gates are opened and the tube grows. We gave in a recent work [Katifori et al., PNAS, 107, 7635 (2010)] a simple physical mechanism to explain the deformation by using simple concepts of Elasticity and Geometry.
Moreover, we were able to demonstrate that pollen grains fold according to very general geometrical rules that could, in principle, be applied to any thin shell structure. Consequently, one line of research in SMAT-C is now to mimic the behavior observed in pollen grains with polymer shells at the micro and macroscopic level, and to investigate how these could be mass-produced as packaging enclosures.

People involved

Eleni Katifori (Rockefeller University)

Jacques Dumais (Harvard University)

David Nelson (Harvard University)

Silas Alben (Georgia Institute of Technology)

Enrique Cerda (Universidad de Santiago)

Geometry of peeled surfaces

Trying to remove wallpaper, adhesive tape, or decal can be a formidable task if the glue underneath is strong. Strips can be removed by tearing down the exposed surface of the film, but they decrease in width and collapse in triangular shapes, so that the process has to be repeated again and again. The basic physical phenomena involved include the fracture of the surface, the detachment from the substrate and the release of mechanical elastic energy in the process of peeling. Our aim is to describe the shapes we have found in experiments and identify how the elastic energy is stored. This knowledge can be used in applications as packaging. Controlling the fracture propagation in a film is an important element in the design of better packaging seals that must resist handling and yet provide a tearing mechanism for easy opening. We have identified a set of crack trajectories leading to divergent tears with potential applications for the industry.